1. Field of the Invention
The present invention relates to a transport means for transporting a recording material and a recording apparatus having the transport means.
2. Description of the Related Art
In recording apparatus, such as a copying machine or a printer, a recording material is generally transported from a sheet feeding station, such as a cassette, through an image forming station and to a sheet eject station. In such cases, conveyance of the recording material is controlled at a predetermined timing as the recording material is led from the sheet feeding station to the image forming station, recorded with an image, and ejected. It is necessary for the transport of the recording sheet material to be precise, especially since the timing of transport from the feed of the recording material to the image recording location influences the image recording position on the recording material. Furthermore, if the conveyance speed of the recording material during image recording is not kept constant, the magnification of the image varies and the image recorded on the recording material is partially expanded and contracted. Slippages among images recorded by the different recording heads therefore occur, especially in the case of an image recording apparatus in which a plurality of image recording heads are disposed side by side. In the case of a color image recording apparatus, such phenomenon results in color slippage and color irregularity, which are critical defects for high-quality image forming. Therefore, it is necessary to precisely drive a transport means and exactly transmit the conveying force of the transport means to the recording material in order to avoid the above problems.
With the above problems in view, various kinds of transport systems have been suggested. For example, a conventional conveyor system conveys a recording material by a pair of rollers and regulates the conveying direction by a guide. Since such a conveyor system feeds the recording material out by pressure between the rollers, the conveying force thereof is strong and the conveyance is reliable and simple. However, the pair of rollers must be placed with the minimum length of a recording material to be used in mind, and such a conveyor system is unsuitable for the conveyance of, for example, postcard-sized and visiting-card-sized recording materials. Furthermore, the system cannot be used in an apparatus, such as an electrophotographic apparatus, where the system cannot be allowed to contact the recording surface of the recording material at any point between the transfer of an image on the recording material by a drum and the fixing thereof.
Another method transports a recording material by nipping and pulling the leading edge of the recording material by a gripper. In this case, once the gripper nips the recording material, the conveying force is surely strong and reliable. However, the mechanism is complicated. Furthermore, the transport system is undesirable in that it is difficult to time the nip of the leading edge of the recording material by the gripper and a mark from the gripper is made on the recording material.
A still further method uses a fan or the like to suck a recording material from the rear of an endless belt with many holes, adhere the recording material to the belt by negative pressure generated by the suction, and convey the recording material. Although this method has been used to convey the recording material prior to fixing of a toner image in electrophotography, since the conveyance is executed by only the suction from the rear, the conveying force is small. Furthermore, it is likely that the surface of the belt will be soiled since dust and toner in the apparatus are also sucked.
In order to solve the above problems, a transport device using an electrostatic suction method shown in FIG. 1 has been suggested by the applicant of the present invention for a color ink jet recording apparatus.
The color ink jet recording apparatus will now be schematically described with reference to FIG. 1. A scanner station 101 reads an image from a document 103 laid on a document table 102 and converts the image into electrical signals and a printer station 201 records on a recording material 203 in accordance with the converted electrical signals. In the scanner station 101, a document scanning unit 104 scans in the direction indicated by the arrow A and reads the image from the document 103. Reference numerals 105, 106 and 107 denote an exposure means, a rod array lens and an equivalent magnification color separation line sensor (color image sensor), respectively. When the lamp of the exposure means 105 is lit during the scanning by the document scanning unit 104 and document 103 is irradiated, the light reflected by document 103 is focused onto the color image sensor 107 through the rod array lens 106, and image information on the document 103 is read for respective colors and converted into digital signals.
In the printer station 201, a cassette 202 feeds recording sheets 203. The feeding operation of the recording sheets 203 stored in the cassette 202 is performed by a feeding roller 202A. The feeding roller 202A feeds recording sheets 203 one by one from the cassette 202 and through conveying rollers 202B. A resist roller 204 temporarily stops the recording sheets 203 at an outlet thereof and then feeds out the recording sheet 203 onto an endless belt 211 in a belt conveyer station 210 according to the document read timing. A recording head unit 220 is composed of a plurality of recording heads 221 for jetting different inks, that is, a head BK for a black ink, a head Y for a yellow ink, a head M for a magenta ink and a head C for a cyan ink. The full-line heads 221 each have an unillustrated ink jet opening disposed corresponding to the recordable width of the sheet and placed at a predetermined space from the endless belt 211.
A recovery cap means 230 is sealed on the jetting openings of the recording heads 221 at non-recording time and recovery time from defective jetting. While a recording operation is performed by the recording head unit 220, the recording head unit 220 and the recovery cap means 230 are maintained in the state shown in FIG. 1, respectively. Reference numerals 240 and 250 denote an eject station for ejecting the recorded sheet 203 after fixing, and an eject tray.
Furthermore, reference numerals 202B, 202C, 202D and 202E denote a conveying roller, a manual supply table, a supply roller and an eject roller, respectively, and reference numerals 202F and 202G denote platens.
The belt conveyor station 210 will now be described in detail. The endless belt 211 (referred to as a conveyor belt hereinafter) is looped between a driving roller 212 and a driven roller 213. A charging roller 214 charges the belt 211 so as to adhere the recording sheet 203 onto the belt 211, a cleaner member 215 is disposed on the exit side of the belt conveyor station 210 and cleans the belt 211 soiled by ink as described below, and a platen 216 is disposed at the rear of the conveyor belt 211 and opposite to the recording head unit 220. A conductive presser member 217 for pressing the recording sheet 203 onto the belt 211 and electrically grounding the recording sheet 203 is mounted on the belt 211 on the entrance side of the belt conveyor station 210.
FIG. 2 shows the construction of the conveyor belt 211. Reference numeral 211A denotes an insulating layer made of an insulating material and which forms the surface of the conveyor belt 211. A conductive layer 211B made of an elastic and conductive material, for example, a conductive rubber or the like, is below the insulating layer 211A. An indented layer 211C is attached to the inside of the conductive layer 211B and has a repeating dent structure.
In the color ink jet recording apparatus having such a construction, the printer station 201 performs a recording operation based on the image information read from the document by the scanner station 101. Then, the recording sheet 203 fed out from the cassette 202 is fed into the belt conveyor station 210 in the timing in accordance with the document reading after being registered by the resist roller 204. The ink is jetted onto the recording sheet 203 at an appropriate timing for recording heads 221 so as to perform a recording operation. Then, the recorded sheet 203 is fixed and ejected onto the eject tray 250 through the eject station 240. A sheet detection sensor 261 is disposed immediately in front of the resist rollers 204 and a sheet detection sensor 262 is disposed in the eject station 240. The resist rollers 204 start rotating in response to a sheet detection signal from the sheet detection sensor 261 or in response to a signal from the scanner station 101 in synchronization with the sheet detection signal, and the resist rollers 204 then feeds the recording sheet 203 into the belt conveyor station 210. The sheet detection sensor 262 confirms ejection of the recording sheet 203, and determines that jamming has occurred when the sheet detection sensor 262 does not detect recording sheet 203 within a predetermined time from when the sheet detection sensor 261 has detected recording sheet 203.
However, because of the sequence of operations in the above recording apparatus, if the recording material 203 jams between resist rollers 204 and the recording head unit 220 in the printer station 201, a recording signal has been already transmitted to each of the recording heads 221, and it is therefore likely that the ink will be jetted onto the conveyor belt 211 in the belt conveyor station 210. Furthermore, since the paper jam is not recognized in this state until the recording sheet 203 reaches the next sheet detection sensor, for example, the ejection detection sensor 262, that recording operation is likely to continue. In this case, large amounts of ink are jetted onto the conveyor belt 211. The conveyor belt 211 is cleaned by the cleaner member 215, which normally does not operate during a recording operation. Thus, during a recording operation a cleaning member thereof (for example, a blade member) is not in contact with the conveyor belt 211. This is because it is necessary to minimize the torque loaded on the conveyor belt 211 during the recording operation since high precision is necessary for the drive of the conveyor belt 211, as described above. Therefore, if the above accident happens during the recording onto a long recording sheet of, for example, A3 size, it is likely that the part of the conveyor belt 211 where the ink is jetted will pass the position of the cleaner member 215 and move downstream, and that the ink adhered onto the part will be transferred onto the charging roller 214 and soil the charging roller 214.
Furthermore, it is also likely that the rear surface of the recording sheet will become soiled since the ink is transferred again from the charging roller 214 onto the conveyor belt 211 during the next recording operation.